1. Field of the Invention
The present invention relates to a fan, and more particularly to a fan having stable pre-loading device.
2. Description of the Prior Art
As shown in FIG. 1(a), the conventional fan 10 includes a stator 20, at least one bearing 30, a rotor 50, a shaft 60 and a spring 70. The rotor 50 further includes a blade structure 55. Besides, the shaft 60 couples the rotor 50 to the bearing 30. As such, the shaft 60 enables the blade structure 55 of the rotor 50 to rotate. The shaft 60 passes through and compresses the spring 70, and then is coupled to the bearing 30. As such, the spring 70 applies a downward force, generally called pre-loading force, on the bearing 30.
Referring to FIG. 1(a) and FIG. 1(b), the bearing 30 is positioned in the bottom of the stator 20. In addition, the bearing 30 is composed of an inner ring 31, a plurality of balls 32 and an outer ring 33. The balls 32 couple the outer ring 33 to the outer periphery of the inner ring 31. During the inner ring 31 rotates respective to the outer ring 33, the balls 32 touch the inner ring 31 as well as the outer ring 33 and thus form the first contact 35 and the second contact 36, respectively. However, the prior art suffers from the problem that the pre-loading force is unstable. For example, the contacts may shift and the pre-loading force fails to be kept constant. The problem and the reason are described in detail as follows. The blade structure 55 may move vertically or horizontally due to some reasons, such as the flow disturbs the blade structure 55. In this case, the spring 70 maybe sometimes compressed and sometimes relaxed. As such, the spring 70 fails to apply constant pre-loading force on the bearing 30, and the first contact 35 and the second contact 36 do not stay at the same positions. As a result, the fan suffers form shake, noise and abrasion.
Besides, prior art fails to adjust the pre-loading force according to the requirement of the user since the spring 70 has been formed previously and thus has no adjustable elastic coefficient.
Accordingly, there has been a strongly felt need for a novel fan having stable pre-loading to solve the above-mentioned problem. Besides, it is desired that the applied pre-loading force is adjustable.
The present invention discloses a fan having stable pre-loading device. Besides, according to the present invention, the pre-loading applied on the bearing of the fan is adjustable. The present fan includes a stator, at least one bearing, a rotor, a shaft, at least one elastic device and a rigid spacer. As shown in the enlarged portion, the stator includes a receptacle having a first thread formed on the inner periphery.
The bearing is positioned in the bottom of the receptacle. In addition, the bearing is composed of an inner ring, a plurality of balls and an outer ring. The balls couple the inner ring to the outer ring. During the inner ring rotates respective to the outer ring, the balls contact the inner ring and the outer ring, respectively.
The rotor further includes a blade structure. The shaft further includes a first terminal and a second terminal. Among these, the first terminal is coupled to the rotor. Therefore, the shaft enables the blade structure of the rotor to rotate. The elastic device (i.e. a spring) is taper and thus including one terminal having major diameter and another terminal having minor diameter. The thinner terminal, having minor diameter, is coupled to the inner ring of the bearing. The rigid spacer formed in the upper section of the receptacle is positioned on the spring and coupled to the terminal having major diameter. The second thread is formed on the outer periphery of the rigid spacer. As such, the second thread and the first thread couple the rigid spacer to the upper section of the receptacle. Besides, the second terminal passes through the central opening of the rigid spacer as well as the elastic device and then is coupled to the inner ring of the bearing. In this manner, the rigid spacer compresses the elastic device.
As described above, the blade structure does not affect the elastic device since the blade structure is separated form the elastic device. The elastic device compressed by the rigid spacer applies pre-loading force on the elastic device. If the distance between the rigid spacer and the bearing is kept constant, the pre-loading force applied on the elastic device is stable since the deformed length of the elastic device is also kept constant. As such, the first contact and the second contact of the bearing are maintained on the same position and do not move with the rotation of the blade structure. That is, the prior problems (i.e. shake, noise or abrasion) caused by the contacts moving with the vibration of the blade structure are effectively improved. Further, in the present invention, the distance between the rigid spacer and bearing is alterable and thus the pre-loading force according to the requirement of user is adjustable.